1. Field of the Invention
This invention relates to a fullerene-added lead zirconate titanate and a method of producing the same.
2. Description of Related Art
As is known from the past, a thin film of lead zirconate titanate (PZT; Pb(Zr,Ti)O3) is used in various products such as a piezoelectric element, a computer memory, an infrared ray sensor, a high permittivity capacitor and the like. In order to prepare the thin film of lead zirconate titanate, there is used, for example, a sol-gel method. According to the sol-gel method, the thin film is produced by forming a solution of a metallic alkoxide or the like in an organic solvent, forming a sot in this solution through hydrolysis and polymerization of a compound, applying the sol onto a substrate, and drying and firing it. In the firing, a temperature of 500-600xc2x0 C. or higher is usually required for producing a perovskite type ferroelectric phase. This is disclosed, for instance, in M. Klee et al., xe2x80x9cDeposition of Undoped and Doped Pb(Mg,Nb)O3-PbTiO3, Perovskite Thin Films on Pt and Conductive Oxide Electrodes by Spin-on Processing: Correlation of Growth and Electrical Propertiesxe2x80x9d, Science and Technology of Electroceramic Thin Films, Kluwer Academic Publishers, 1995, p.99, and K. Miyazawa et al. xe2x80x9cStructure of Duplex Multilayer Pb(Zr0.53Ti0.47O3) Films Prepared by Sol-Gel Processingxe2x80x9d, J. Am. Ceram. Soc., 81(1998) p.2333.
However, the above conventional sol-gel method conducts the firing at such a high temperature, and has problems that the composition of the PZT film is shifted by diffusing a metal of an electrode formed on the substrate into the inside of the film and that a large thermal stress to peel off the PZT film is easily caused between the substrate and the PZT film. And also, when the PZT film used as a piezoelectric actuator in a microdevice is formed by the sol-gel method, such a high firing temperature results in the deterioration of the properties in the other elements or the electrode junctions incorporated into the same substrate.
The invention is to advantageously solve the above problems and to propose a novel method of producing PZT capable of effectively producing a perovskite phase at a temperature lower than the conventional one in the production of PZT through the sol-gel method as well as PZT obtained by this method.
The inventors have made various investigations in order to achieve the above object, and found that it is very effective to add a fullerene typified by C60 as an auxiliary material to PZT sol for achieving the above-mentioned object.
The invention is based on the above-mentioned knowledge.
The invention lies in a method of producing a fullerene-added lead zirconate titanate which comprises dissolving zirconium alkoxide, titanium alkoxide and lead acetate in an organic solvent with a stabilizer to form a colloidal solution (sol), adding a fullerene thereto, gelatinizing, drying and firing them at a relatively low temperature.
In the production method according to the invention, a preferable firing temperature condition is about 400xc2x0 C. to about 500xc2x0 C.
And also, it is favorable that the fullerene-added lead zirconate titanate according to the invention can easily be produced when the zirconium alkoxide is zirconium tetra-n-propoxide and the titanium alkoxide is titanium tetraisopropoxide and the stabilizer is diethanolamine. Moreover, in the production according to the invention, the alkoxide as a starting material is not restricted to the aforementioned one and various alkoxides can be used in the starting material for lead zirconate titanate. Further, in the method of the invention, various alcohols and toluene are advantageously adaptable as the organic solvent.
The fullerene-added lead zirconate titanate obtained according to the invention can take various forms including not only thin film but also powder or bulk body. In the case of producing the thin film, the colloidal solution is added with the fullerene and coated onto a substrate.
In the fullerene-added lead zirconate titanate produced according to the invention, the fullerene is well dispersed in lead zirconate titanate. And also, when the thin film of the fullerene-added lead zirconate titanate according to the invention is formed on the substrate, [100] in perovskite phase is strongly oriented to obtain good ferroelectric properties. The fullerene dispersed in lead zirconate titanate contains at least one material selected from the group consisting of C60, C60 polymer and carbyne.
The ratio of fullerene in the fullerene-added lead zirconate titanate according to the invention is preferably about 5-30 vol %, more desirably about 10 vol %.